Analysts expect Perth-based SSE to announce bumper profits for the second year running. Photograph: Andrew Milligan/PA

Accusations that the big energy firms are profiteering at the expense of UK households will be centre stage again on Wednesday if Scottish & Southern Energy, as expected, reveals bumper profits for a second year running.

Analysts are predicting the Perth-based company, which supplies 9.6m households with gas and electricity, could announce profits as high as £1.4bn for the last 12 months – a 5% rise on the previous year.

It will also heap more pressure on both the government and Ofgem, who have been accused of standing by as the big six suppliers profit at their customers' expense.

Last October SSE raised domestic energy prices by 9% to coincide with the start of the coldest and longest winter of recent years. A few weeks later it revealed that it had made £397.5m in the six months to the end of September, compared with £287.4m in the previous year – a 38% increase for that period.

SSE is not alone in announcing startling results. National Grid recently posted a £2.7bn profit on revenues of £14.4bn – a margin of about 19%. British Gas said an increase in gas usage of 18% in the first four months of 2013 due to very cold weather had helped its figures. Its parent company, Centrica, is on target to post full-year earnings of £1.4bn, prompting the Fuel Poverty Action group to target the companies recent AGM with its Stop the Great Fuel Robbery campaign.

Mark Todd, director at price comparison service, energyhelpline, said the profits at National Grid needed to be addressed by the government. "This is the kind of margin normally associated with successful high-risk activities, not with running a low-risk infrastructure businesses that have a captive market. The attention really must turn to how consumers can get a better deal from the energy market."

He said typical household gas prices have risen 173% over the last 10 years and warned that despite the much publicised Downing St summits, only a few million homes are on the best deal possible, with over 20m household still overpaying.

Elizabeth Ziga, of the Fuel Poverty Action group, said: "While SSE customers were skipping meals to keep the heating on, the company continued to rake in bumper profits. To end this chilling profiteering, we have to break the big six's grip over our energy."

Last week the Department for Energy and Climate Change warned there were 4.5 million people in fuel poverty in 2011. Since then, campaigners have warned, their number will have risen as prices and consumption have jumped this winter. Many household have still had their heating on this week.

Meanwhile, Wednesday's results at SSE will include the latest numbers on compensation for mis-selling. In April the regulator Ofgem cited a "woeful catalogue of failures by the SSE management" that led to years of mis-selling over the phone, in stores and on customers' doorsteps. SSE stopped door-to-door sales in 2011, but such practices persisted in its other sales channels until September 2012.